The overall goal of this project is to define the catalytic properties of the [unreadable]-subunit of the voltage-sensitive potassium channel (Kv). The Kv channels regulate cell excitability and have been shown to play an important role in oxygen-sensing, volume regulation, memory, and learning. The Kv[unreadable] proteins are ancillary proteins that associate with the cytoplasmic domain of Kv channels, but no clear physiological function has been assigned to these proteins. Structural and sequence analyses show that Kv[unreadable] proteins are members of the aldo-keto reductase superfamily. Our central hypothesis is that the Kv[unreadable] proteins catalyze the reduction of endogenous carbonyls whereby they impart redox sensitivity to Kv currents. Such regulation may be an important feature of oxygen-sensing or metabolic dependence of Kv currents. To test this hypothesis we will measure the catalytic efficiency of Kv[unreadable] proteins with endogenous substrate series consisting of prostaglandins, steroids, metabolites of neurotransmitters and lipid peroxidation products. We will also test whether assembly of Kva-[unreadable] complexes enhance enzymatic activity of Kv[unreadable] and determine the sequence and rate-limiting step in its catalytic cycle (Aim 1). To determine whether the endogenous carbonyls utilized by Kv[unreadable] in biochemical experiments, are also functionally active, we will examine the ability of the most efficient series to alter the voltage-sensitivity and the kinetics of Kva-[unreadable] channels expressed in COS-7 cells (Aim 2). Results of these experiments will allow us to distinguish whether nucleotide binding itself, catalytic cycle, or binding of ligands which can serve as pharmacologic agents modulate Kv inactivation. Taken together, the findings of this study will provide a better understanding of the catalytic and ligand binding properties of Kv[unreadable] and form the basis of a more in-depth project to examine the in vivo role of Kv[unreadable] catalysis and its putative role in regulating surface excitability, oxygen-sensing, or encoding memory. Results of these studies could also form the basis of developing pharmacological modulators of Kv[unreadable]-mediated changes in Kv current.